The vestibular system, whose sensory signals originate in the labyrinth of the inner ear, plays an important role in the maintenance of normal posture. This research is designed to explore (a) how, during normal head movements, the various sensory signals coming from the labyrinth encode the spatial and temporal properties of the head movement, (b) how these signals are combined and processed by neurons in the brainstem vestibular nuclei, (c) with information is sent to various spinal motor pools to produce coordinated reflexes (for example, signals to the neck to maintain head orientation, signals to the limbs to maintain erect posture), and (d) how this information is integrated with other sensory and motor information in the balance control system. These experiments will employ the cat animal model, as much has already been learned about the neural pathways of importance in this system. Recordings will be made from single identified neurons at various levels (e.g. vestibular nerve, vestibular and other brainstem relay nuclei). Responses to controlled three- dimensional movements of the animal will permit an identification of the types of vestibular input present. Experiments are designed to study the interaction of the vestibular signals from the semicircular canals and the gravity-sensing otolith organs, the interaction between vestibular and other sensory systems, and the neural processing mechanisms which produce the observed transformed signals.